In the search for new antibiotic substances, a general method that would permit the prompt recognition of new types of antibiotics (i.e., antibiotics with different mechanisms of action) and at the same time reduce the risk of under-taking costly investigation of an unidentified substance which may not be new would clearly be advantageous. A means for achieving this purpose was sug-gested some time ago (Stansly, 1946). It was proposed that strains of bacteria specifically resistant to the various known antibiotics should be prepared from one or more designated parent strains, and the resistant strains then filed with an agency, such as the American Type Culture Collection, in order that they might be readily accessible and available upon request. Strains of bacteria specifically resistant to the known antibiotics would enable investigators to determine in a systematic fashion very early in an investigation whether an unidentified antibiotic was different from or similar to any one of the known substances. This will be elaborated upon further and examples illustrating the method described